January 26, 2001, the Republic Day (Bhuj) earthquake of Kachchh and active faults , Gujarat, western India Javed N. Malik * , Takashi Nakata * , Hiroshi Sato *3, Toshifumi Imaizumi * , Toshikazu Yoshioka , George Philip *6 A. K. Mahajan* 6, and R. V. Karanth* Abstract The Kachchh falls under seismically active zone-V outside the Himalayan seismic belt, and forms a part of Stable Continental Region (SCR). In the span of 50 years the Kachchh has experienced two large magnitude earthquakes, i.e. the July 21, 1956 Anjar with ML 7 and the 2001 event with Mw 7.6. No coseismic surface rupture was associated with the Bhuj earthquake, suggests movement along a blind thrust has resulted into extensive lateral spreading of water saturated near surface soil horizon giving rise to formation of numerous E- W striking extensional cracks or normal faults and the longitudinal pressure ridges in the epicentral area around Budharmora and Morgar villages. Liquefaction in the low-lying areas comprising fine sediments was the common phenomenon observed during this earthquake. By satellite photo interpretation several traces of active faults were identified for the first time occurring in the pediment zones along the northern margins of Katrol Hill Range and Northern Hill Range respectively. The active faults have displaced along them the Late Quaternary alluvial fan deposits and colluvial debris, resulting into formation of the north facing fault scarplets. Our field observations reveal that none of the active faults have moved this time. Thus, it is suggested that these faults still have high potential to break large magnitude earthquake in future. and measured a local magnitude ML 6.9, depth 15 km (Fig. 1). Introduction This is the most devastating earthquake in the history of India, in the sense of causalities and destruction. There are records of At 8:46 a.m. (1ST) on January 26, 2001, when people of India such large magnitude events those struck Kachchh in the recent were celebrating the Republic Day, a large earthquake of Mw past, the well known amongst them are of 1819 Allah Bund, ML 7.6 broke out in the western part of Gujarat, India, causing vast 8 and 1956 Anjar, ML 7. Though these two events were of destruction and causalities. The event lasted for more than 30 magnitude above M 7, number of causalities reported was much seconds. Epicenter of the mainshock reported by the USGS to be less, about 2000 killed during the 1819 and only 115 fatalities 23.36 ° N and 70.34 ° E, Mw7.5, depth 22 km and the University and hundreds were injured by the 1956 quake. The main reason of Tokyo, suggests Mw 7.6; 23.40 ° N and 70.30 E, depth 18 for rising toll of the deaths and total destruction during the km. However, the Indian Meteorological Department located the present earthquake is the rapid increase of population in the area. epicenter 23.6 ° N and 69.8 ° E, in the Great Rann-Banni Plains, More than 19,000 people are reported to have been killed and * 1 JSPS Fellow at Department of Geography * 5 Active Fault Research Center , Hiroshima University, Japan , AIST-GSJ, Japan * 2 Department of Geography , Hiroshima University, Japan Wadia Institute of Himalayan Geology, Debra Dun, India *3 University of Tokyo , Japan *7 M. S. University of Baroda, Vadodara, India * 4 Yamanashi University , Japan over 160,000 injured by this earthquake (Jain et al., 2001) identification of surface rupture resulted by the present quake However, according to the local people of Kachchh the toll of and to collect the ground truth of active fault traces (identified deaths is much higher than the figure declared officially. Many with help of satellite photo interpretation by Malik and Nakata, of them stated that, still the dead bodies are lying buried under before this quake), (2) to verify whether any active fault moved the debries, which are not recovered, this was the situation or was the source for this earthquake and (3) to record the almost after a month passed. News agencies have mentioned that magnitude of damage in and around the epicentral area. about 600,000 people are left homeless due to this quake. The Since the active faults identified were only the active tectonic Gujarat State Government has estimated loss of about US $ 5 features in the area, we presumed that one of them was probably billion i.e. around Rs. 22,000 Crores (Jain et al., 2001). the source of the Bhuj earthquake. However, our field The source of the earthquake is not yet correctly located. observations revealed that none of the active faults moved Numerous studies carried out after the earthquake suggest that during this earthquake. It is, however, difficult to yet pinpoint probably the movement took place on a blind thrust, and the exactly which fault moved in sub-surface. rupture did not reached to the surface. Also it not fully We present here a preliminary report on the field observations understood whether the earthquake was an interplate or and aerial survey, highlighting active faults identified along the intraplate type. Kachchh Mainland Fault, surface deformation formed during A short fieldwork and aerial survey was undertaken in this quake and degree of damage in the epicentral area and its Mainland Kachchh along Kachchh Mainland Fault Zone and vicinity. We expect that this information will be useful to Katrol Hill Fault Zone by our team between February 27 and evaluate the seismic hazard assessment for future and to March 5, 2001. Our prime emphasis was: (1) towards understand the nature and pattern of faulting. manifestation of complicated flexures along the bounding faults Geomorphic and Tectonic Setup and by secondary uplifts. Tertiary and Quaternary succession with mainly coastal plain and fluvial structures border these The Kachchh peninsula marks the western continental passive uplifts. Satellite photo interpretation as well as field studies margin of northward drifting Indian plate (Fig.1). The basic suggest that the area has been experiencing intense folding and structural framework of Kachchh represents a rift basin, which these folded structures show its strong control over the present dates back to Late Triassic-Early Jurassic, exhibiting the longest landscape. record of the Mesozoic succession in the western India (Biswas, Geomorphologically, the Kachchh can be categorized into four 1987). This rift basin is now under the influence of major E-W trending zones (1) coastal zone demarcating the compressional stress regime resulted due to the collision of southern fringe, (2) Kachchh Mainland forming the central Indian and Eurasian plates. The landscape of Kachchh shows a portion of rocky uplands, (3) Banni-Plains marked by raised complex structural pattern marked by uplifts (Kachchh mud flats and (4) Great Rann in north and Little Rann in the east Mainland) and low-lying residual depression (Great Rann-Banni comprising vast saline-waste land. The boundaries of these plains). Uplifts are confined along the major sub-parallel E-W geomorphic zones are bounded by major faults (Fig. 2). striking longitudinal faults (Fig.2 ), e.g. the Katrol Hill Fault, Morphology and structure of Kachchh Mainland and Great Kachchh Mainland Fault, Banni Fault, Island Belt Fault and Rann-Banni plains: Allah Bond Fault (Biswas and Deshpande, 1970; Biswas, 1980). Kachchh Mainland comprises two major hill ranges viz. The The general form of deformation and uplifts are marked by Northern Hill Range and the Katrol Hill Range (Fig. 3a, b). Both domes and asymmetric anticlines exposing the folded Mesozoic these ranges are flanked to their north by major E-W striking rocks (Middle Jurassic-Lower Cretaceous) in the Kachchh longitudinal faults, Kachchh Mainland Fault and Katrol Hill Mainland (Biswas, 1980; Malik et al., 2001). The uplifts, Fault respectively. These hill ranges are characterized by however, are not simple broad-topped upwarps, but are the monoclinal flexures, anticlines and cuestas aligned along the southern flanks of the E-W trending faults. are seen resting unconformably on the Mesozoic E-W and WNW-ESE striking Kachchh Mainland Fault mark sandstone+shale succession, with thickness upto 3 to 15 m and the northern margin of the Kachchh Mainland, where the are probably of Late Quaternary age . Northern Hill Range with average altitude between 130 to 388 m The Katrol Hill Range with average altitude of 148 to 348 m abuts against the low-lying Great Rann-Banni plains. The flanked to its north by Katrol Hill Fault marks the major deformational pattern of this hill range is characterized by steep drainage divide in the Kachchh Mainland (Fig. 3a). Uplift and north facing escarpment and gently south dipping Mesozoic deformation of this range along the Katrol Hill Fault has strata. According to Biswas (1980), the Kachchh Mainland fault controlled the development of numerous north and south flowing is a vertical to steeply inclined normal fault at depth, and rivers (Malik et al., 2001). The morphology of deformation in changes to a high angle reverse fault near the surface. The this fault zone is similar to that along the Kachchh Mainland geomorphic expression suggests a phenomenon of fault- Fault. Intense asymmetric folding of the Mesozoic and Tertiary propagation folding as described by Suppe, (1983). It is also bed rock has given rise the range with north facing steep suggested that the movement is taking place along a south forelimb with gentle back lime due south. Folding in Middle dipping low angle reverse fault. Several semi-conical alluvial Pleistocene Miliolitic rocks (Sohoni et al., 1999), suggests that fan lobes developed by numerous north flowing rivers similar deformation has been continued during Upper- debouching into Great Rann-Banni depression occupy the Pleistocene to Holocene. The pattern of micro-seismicity also pediment zone along this range (Fig.